Demand for high speed data services, especially downlink data services, fuels a need for increasing the volume of information simultaneously supported by a radio access node within a given region. Mobile wireless devices are increasingly being used to provide a variety of data streams, in the form of music and video programming, etc. Moreover, increased mobile wireless user equipment density, especially in urban environments, place additional pressures upon service providers to boost downlink data bandwidth to meet user demand for greater and greater downlink data rate limits.
New radio access technologies, providing sub-channels through spatial multiplexing of a shared frequency spectrum on a download link, are presently being developed based on massive MIMO antenna array structures comprising a plurality of individual antenna elements. Rather than radiate an omni-directional signal, groups of antenna elements of the massive MIMO antenna array structures are driven/controlled to support beamforming. Simply put, beamforming is a signal transmission technique where a same signal is transmitted (with appropriate amplitude and phase modulation) by a group of transmitters such that constructive/destructive interference results in a signal that is effectively transmitted as a beam in a particular angular direction—as opposed to radiating in all directions from a single antenna element.
Beamforming enables a single massive MIMO antenna array structure to support space-division multiple access (SDMA) simultaneous communication with multiple receivers. Such spatial multiplexing enables simultaneous downlink data streams via distinct signal beams connecting the transmitter (massive MIMO antenna structure) and receiver (e.g. user equipment). Precoding, which is paired with appropriate decoding at the receiver, is applied to the individual antenna elements to render the plurality of distinct signal beams supporting downlink data transmissions between the massive MIMO and user equipment.
Given the directional focusing of a signal arising from beamforming at the signal source (i.e. the RAN), enhanced channel status monitoring ensures that acceptable signal quality is maintained for mobile user equipment that receive downloaded information via the directional signal beams transmitted by the sub-groups of antenna elements of the massive MIMO antenna structure.
Knowledge of channel state information is an important element of successful implementation of data transmission schemes carried out by the massive MIMO antenna technologies. The “spatial” aspect of implementing SDMA multi-user schemes at the massive MIMO structures enhances the importance of maintaining an accurate and up-to-date CSI status for each of the multiple user equipment downlinks (i.e. directionally focused transmission beams) simultaneously supported by the massive MIMO implementing SDMA.